Metal closures are produced by a rapid metal stamping operation, which forms the shell, followed by a multistep conversion operation during which the pull tab is formed and attached to the shell. In a standard conversion press the upper conversion die vertically reciprocates at over 300 cycles per minute while a conveyer holding closures in individual magazines, indexes the closures through the press in synchronized relation with a narrow width tab stock.
In one type of conventional press, after the conversion operation is completed, the finished closure continues being indexed forward in its individual magazine to an upstacking station. When the conveying belt stops for the next operation by the conversion die, a reciprocating stacking member moves upwards through the magazine in the conveying belt, and into contact with the bottom surface of the closure, pushing the closure upward into a receiving station. The reciprocating member then moves downward to a position below the conveying belt and the belt is indexed forward for the next conversion die operation.
Many presses have a testing station immediately upon exit from the press. A tab sensing means checks each closure for a tab to assure the press is properly operating. Upon encountering a closure without a tab, the press immediately shuts down so corrective action may be taken, which generally involves the rethreading of a new roll of tab stock into the press.
The tab stock is threaded through the press by "inching" the press forward at a very slow rate of speed until tab stock is present throughout the multiple stations. As the press is "inched" forward, closures which do not have pull tabs are exited from the press until the tab stock is threaded throughout the press. Removal of these defective closures between the exit of the press and the upstacking station is generally impossible due to lack of access and such removal must be delayed to a downline station where access to the closure line is more readily achieved.
Furthermore, due to the dynamics of the press operation and the design for high-speed operation of around 300 cycles per minute, it is often difficult to assure quality stability of the closures produced after threading and during start-up of the press until regular operating speeds are reached. Typically, in slow-speed operation, the press will provide a smaller depth scoreline around the removable portion of the closure thereby requiring higher opening forces to tear the pull tab from the closure.
In the past due to the difficulty in accessing closures between the exit of the press and the upstacking means, closures without pull tabs, and when desired, closures produced during start-up, have been manually removed from the production line downstream of the upstacking device.
This is generally done by marking the first bad closure with a colored ink and after starting the press and a period of operation, finding the marked closure as it passes an accessible downline location and removing it along with an estimated number of subsequently produced closures. This method is time consuming, messy, inefficient, wasteful and leaves room for error should the defective closures be missed or forgotten.
U.S. Pat. No. 2,361,960 to Pelosi, discloses an upstacker with reject means wherein rejection is accomplished by restraining the upward movement of the stacking member with a solenoid actuated pawl.